1. Field of the Invention
The present invention relates to an optical wavelength conversion device.
2. Description of the Prior Art
There is an optical wavelength conversion device having an essential structure as shown in FIG. 1. The wavelength conversion device comprises a semiconductor laser 1 and a wavelength conversion element 5 of optical fiber type. The semiconductor laser 1 is used as a light source generating a fundamental wave. The optical wavelength conversion element 5 has a core 3 made of nonlinear optical material and a clad 4 surrounding it. The wavelength conversion element is used as a waveguide type wavelength conversion element for converting the fundamental wave having a wavelength to the secondary harmonic having a half wavelength of the fundamental wave. This optical wavelength conversion device further has a condenser lens disposed between the semiconductor laser 1 and the wavelength conversion element 5 which is employed for converging the fundamental wave emitted from the semiconductor laser 1 to an optical coupling portion i.e. a circular end surface(core end surface) of the core 3.
It is necessary to efficiently couple the fundamental wave to the optical coupling portion of the core end surface in order to convert the fundamental wave to the secondary harmonic with a high efficiency in the optical wavelength conversion device. For this purpose, a focused spot of the fundamental wave emitted from the semiconductor laser 1 should be accurately aligned with the core end surface receiving the focused spot in the three dimension, i.e. X and Y directions on the core end surface and in Z direction of a standard optical axis of the core. Here, the direction of the standard optical axis is Z direction in the rectangular XYZ coordinate system as shown in FIG. 1.
In this case, the adjustment accuracy in the Z direction is determined by the focal depth of the condenser lens 2, and an error of about .+-.1 .mu.m is allowed.
However, the relative position between the focused spot of the fundamental wave and the core end surface receiving the focused spot should be adjusted with a fine accuracy at a submicron order during the aligning operation of the X and Y directions on the core end surface, because the diameter of the core 3 is about 1 .mu.m.
It will be presumed that the optical wavelength conversion element 5 and/or the condenser lens 2 are mounted on a fine-movement stage of an adjusting mechanism so as to perform a fine adjustment between the fundamental wave and the core end surface in X and Y directions with a high accuracy.
However, it is difficult to satisfactorily achieve such a high-accuracy adjustment. Further, the fine adjustment as described above leads to a complicated adjusting mechanism, and this hinders the preparation of a small-size optical wavelength conversion device. This further results in inconveniences for mass production and cost reduction.